INVESTIGATION OF THE CONFORMATION OF HYLTHIO)-2,4-DITHIOXO-1,3,2,4-DITHIADIPHOSPHETANE, (CH3S)2P2S4, BY CRYSTAL-STRUCTURE DETERMINATION, VIBRATIONAL ANALYSIS AND QUANTUM-MECHANICAL CALCULATIONS

hylthio)-2,4-dithioxo-1,3,2,4-dithiadiphosphetane, (CH3S)2P2S4 (called Davy reagent methyl) has been characterized by X-ray crystallography. The central part of the molecule is a P2S6 unit similar to that of th e metathiodiphosphate anion P2S6 The methyl groups are arranged in a ' 'trans-closed'' configuration that is quite remarkable. By energy calc ulations at the 6-31G/MP2 level it is shown that the observed conform ation has the lowest energy, but the discrimination is small and is co unteracted by entropy effects. The Raman and IR spectra have been reco rded, and the vibrational frequencies assigned to the ''trans-closed'' form of the molecule present in the crystal structure. Some additiona l bands have to be attributed to conformers. In the Raman spectrum of the title compound dissolved in trichlorbenzene, the ''trans-out'' con former dominates, hence packing effects influence the conformation.